Haul Out…. what the zinc is going on?

Every two years or so I haul the boat out of water so that the bottom can be painted with a type of paint that inhibits growth of algae and other things that might otherwise be inclined to establish a home on the hull of my vessel. This year, I also planned to have the boat polished and to “glass over” two instrument through holes in the forward part of the vessel. The latter process includes sealing the channel with epoxy and laying fiberglass in and over those areas so that the holes are permanently sealed.

Rudder looking aft. The greenish disc is a ground for the SSB radio.

The folks at KKMI called me as soon as Skiron was out of the water. They were concerned regarding tell tale signs that the vessel had too many zinc anodes. These are photographed below. The findings are more common on steel and wooden vessels but can be seen with fiberglass hulls as well.

Zinc anodes are placed on a boat to prevent rust of parts in the water that are made of iron. The zinc anode deteriorates in place of the important ferrous parts. A common problem with vessels is too little zinc….or failure to replace depleted zinc and loss of protection. Even though intuition might lead one to believe that the more zinc the better this is clearly not the case….as I have just learned!

KKMI, and the boat electrical consultant, suggested that we remove all but the zinc anodes associated with the propeller shaft and the bow thruster. I will have a diver inspect the boat periodically and we will determine whether to add back any of the anodes.

Paint and primer gone around anode that had very little oxidation.
Primer and paint near anode blown or burned off. Zinc looks oxidized such that it may not be effective but I’m not really sure.
Zinc anodes at 50% are essentially expended. The anode looks properly depleted to me. Paint loss likely due to excess anodization.

Here’s a nice article on excess zinc anodes.


Here’s a nice article with an introduction to marine corrosion.


Check out this link to learn more about KKMI.


Here is a book recommendation……

Cleaned. Primed. Painted. Unneeded through hulls glassed over. Hull polished. Excess zinc anodes removed. Ready to launch!
Fore cabin bilge much more tidy with two unnecessary through hulls epoxied and glassed over inside and out.
Magnificent work by KKMI!!

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